1. Field of the Invention
The present invention relates to a method of and an apparatus for driving a turbosupercharger wherein an exhaust gas turbine is driven with the exhaust gas energy of an internal combustion engine and is used for actuating a supercharging turbine, thereby to supercharge the engine with suction air.
2. Description of the Prior Art
There has been well known an exhaust gas turbine-supercharging system wherein an exhaust gas turbine is rotated by utilizing exhaust gas energy, thereby to drive a supercharger so as to supercharge an engine with suction air. Particularly in recent years, examples of the supercharging system installed on the engines of automobiles have increased.
A turbosupercharger in the prior art is usually constructed of only one stage of centrifugal turbine, the power of which is obtained in such a way that exhaust gas brought out of the combustion chamber of an engine is partly or wholly passed through an exhaust gas turbine so as to change the kinetic energy thereof into a rotational motion. The supercharging turbine supercharges the combustion chamber with suction air at a heightened density together with vaporized fuel.
The prior-art system mentioned above, however, incurs the following problems:
1) A time lag is involved before a turbo effect develops.
2) A sudden change in the output of the system is induced by the turbo effect.
3) Maximizing phenomena in which a boost pressure and engine r.p.m. (revolutions per minute) reach the maximum values, appear early.
4) The overheat rate of the engine is high.
5) The efficiency of fuel consumption is prone to worsen.
The inventor made studies on these problems. The problem 1) of the time lag is considered ascribable to the fact that, at the initial stage of the operation of the system, the pressure (back pressure) of the exhaust gas is insufficient on account of a low-speed rotation and the fact that a torque required for starting the exhaust gas turbine is not attained quickly. The problem 2) of the sudden output change is considered ascribable to the rapid rise of the back pressure and the inertia of the rotation.
The problem 3) of the maximizing phenomena is considered ascribable to the fact that the exhaust gas turbine becomes incapable of absorbing the exhaust gas energy sufficiently. The insufficient absorption will be influenced by the nonuniform velocity distribution of exhaust gas streams passing through turbine blades, the occurrence of surging, the inferior emission efficiency of the exhaust gas after passing through the turbine, and so forth. The efficiency of the gas emission is drastically lowered by the very long pipe of an exhaust system, a catalyst, a muffler, etc. Moreover, on account of the decrease of the air density attributed to the exhaust gas at high temperatures, the mean effective pressure (P.sub.m) is conspicuously lowered especially in case of a gasoline engine, so that part of the boost effect is canceled. Suction air cooling is required for coping with the decrease of the air density. Meanwhile, the overheat of the engine in the problem 4) becomes liable to occur when the whole engine has a tendency to overheat at all times. Therefore, the overheat is caused by heat which accumulates in peripheral devices due to return flow heat from the supercharger at high temperatures and the low emission efficiency. Further, the efficiency of fuel consumption in the problem 5) will worsen particularly in consequence of the fact that the operation of the system is excessively repeated with the intention of bringing out the turbo effect.
Upon such studies, the inventor has come to the conclusion that the supercharging system in the prior art will be demeritorious in point of the method wherein, in driving the exhaust gas turbine of the supercharger, only the kinetic energy of the exhaust gas streams from the combustion chamber is utilized. One reason therefor is as follows: No demerit will be incurred if the energy of the exhaust gas which is so fast as to exceed the speed of sound can be utilized for the drive of the exhaust gas turbine as it is. Since, however, a high load resistance exists in the lower stream of the exhaust system, the energy of the exhaust gas cannot be sufficiently utilized. Therefore, when the emission efficiency can be equalized to a value in the absence of the resistances of the catalyst, the muffler, etc., the demerit of the insufficient utilization of the exhaust gas energy ought to be solved. Moreover, when the emission efficiency can be enhanced, the problem of the accumulation of heat is relieved, and hence, the enhanced emission efficiency can contribute also to the solution of the heat problem.
The present invention has been made in view of the above circumstances, and has for its object to provide a method of and an apparatus for driving a turbosupercharger in which an exhaust gas turbine is driven under a positive pressure by exhaust gas streams having undergone almost no load resistance, while at the same time, exhaust gas streams having passed through the turbine are drawn off under a negative pressure by suction air streams of lower pressure, whereby the emission efficiency of exhaust gas can be remarkably heightened, thereby to eliminate the aforementioned disadvantages.
In order to accomplish the object, the emission efficiency in the vicinity of the supercharger is intended to become equal to or greater than a value in the absence of a load resistance in an exhaust system.
In a turbosupercharger wherein an exhaust gas turbine is driven with exhaust gas energy, and a supercharging turbine is actuated by the exhaust gas turbine so as to supercharge an engine with suction air the present invention for accomplishing the object adopts a technical expedient in which exhaust gas streams are introduced into a turbine inlet of the exhaust gas turbine, thereby to drive the exhaust gas turbine under a positive pressure, and exhaust gas streams having passed through the exhaust gas turbine are drawn by suction with suction air streams of lower pressure, thereby to simultaneously drive the exhaust gas turbine under a negative pressure.
Regarding the suction air streams, the negative pressure generated by accelerating the exhaust gas streams can be obtained as power, and it is best to utilize this power. Although the negative pressure can also be formed by utilizing electric power or the rotation of a shaft, the output of the engine is reduced at a very high rate on that occasion.
In addition, the method described above should desirably be performed by an apparatus for driving the turbosupercharger, said turbosupercharger including the exhaust gas turbine which has the turbine inlet for introducing the exhaust gas streams emitted at high speed from a combustion chamber of the internal combustion engine and which is driven under the positive pressure by the exhaust gas streams having flowed through the inlet, as well as the supercharging turbine which is actuated by the exhaust gas turbine, comprising an exhaust system pipe which is connected to a turbine outlet for leading out the exhaust gas streams having passed through the exhaust gas turbine and which serves to emit the exhaust gas streams into the atmosphere, a negative pressure generator which is disposed at a part of the exhaust system pipe immediately preceding the emission of the exhaust gas streams into the atmosphere and which accelerates the exhaust gas streams into high-speed air streams again so as to form negative pressure of high intensity, and a suction path which brings the negative pressure generator and the turbine outlet side into communication in order to drive the exhaust gas turbine by the use of the negative pressure formed by the negative pressure generator.
According to the method and apparatus of the present invention, a resistance which the exhaust gas streams passing through the turbosupercharger undergoes is conspicuously decreased, and the r.p.m. of the engine are sharply increased, so that the flow velocity of intake air passing through the supercharging turbine is remarkably heightened to markedly enhance the efficiency of charging. As a result, heat of the exhaust gas which otherwise overheats the supercharge is quickly carried away, so that the supercharger does not fall into an excessively heated state. Moreover, the temperature of the suction air becomes relatively low, so that the air density rises. Also from this viewpoint, the efficiency of charging is heightened.